The present invention relates to methods and devices for adjusting the braking and/or driving effect at the wheels of a motor vehicle.
Such systems are known, for example, as anti-skid systems, traction control systems or vehicle stability systems. These systems have in common the fact that the adjustment of the braking and/or driving effect at the motor vehicle wheels is at least dependent on the detected wheel speeds. These wheel speeds are generally detected by wheel speed sensors. In this connection, emergency measures must be provided for the event that one or more wheel speed sensors are defective. German Published Patent Application No. 34 17 019 describes a circuit arrangement for a traction-controlled vehicle-braking system, the braking pressure control at the wheel having the defective sensor being dependent on the rotational characteristics of the front wheel on the same side in the event of a failure or a malfunction of a rear wheel speed sensor. From European Patent No. 0 814 983, it is known that in the event of a failure of a rear wheel speed sensor signal, the vehicle speed reference signal or the vehicle speed signal itself is used as a substitute signal for the defective speed signal.
If there is tire damage on a motor vehicle, often only a light-weight spare wheel or spare wheel is provided. In contrast to the standard wheels, such a light-weight spare wheel or spare wheel has a significantly smaller diameter. The detection of such light-weight spare wheels or spare wheels is known from European Patent No. 0 449 845.
A mulitplicity of measures is known for checking the function of speed sensors or for the error recognition of speed sensors. As an example, reference should be made to European
The present invention relates to methods and devices for adjusting the braking and/or driving effect at the wheels of a motor vehicle having at least four wheels mounted on at least two axles. Sensors are assigned to these wheels which detect the rotational movements of the wheels. The adjustment of the braking and/or driving effect is activated at least as a function of the output signals of these sensors. Moreover, it is determined according to the present invention whether a spare wheel, i.e., a wheel having a smaller diameter than the other wheels, is mounted. In addition, defects in the sensors are determined. In response to the detection of a defect in one sensor, in accordance with the present invention, the adjustment of the braking and/or driving effect at the wheel of an axle assigned to this sensor is activated as a substitute as a function of the detected rotational movement at the wheel of another axle on the same side.
According to the present invention, the substitution by the wheel speed sensor on the same side is only activated if it is determined that this wheel on the same side is not a spare wheel. Taking the possible mounting of a spare wheel into account increases the quality of the substitution measure. If the wheel on the same side were namely a spare wheel, the substitute signal for the failed sensor would represent an incorrect rotational movement at the wheel at which the sensor had failed.
According to the present invention, the sensor signal at the wheel of the other axle on the same side is only used as a substitute when it is determined that such wheel is not a spare wheel. If, however, a spare wheel is mounted to the other axle on the same side as the failed sensor, then according to an advantageous embodiment of the present invention, the output signal of the sensor on the other wheel of the same axle is used as a substitute signal. In response to the determination of a defect in one sensor, the adjustment of the braking and/or driving effect at the wheel of an axle assigned to this sensor is then activated as a substitute as a function of the detected rotational movement at the other wheel of the same axle if it is determined that the wheel of another axle on the same side is a spare wheel. In this manner an effective emergency measure is obtained even if a spare wheel is mounted to the wheel of the same side.
A further embodiment of the present invention assumes that at least one wheel is driven by a drive unit via the drive train of the motor vehicle. In this connection, a rotation quantity is detected which represents a rotational movement in the drive train. This rotation quantity may, for example, represent the output speed of the drive unit, in general of the vehicle engine and/or the input and/or the output speed of a transmission arranged in the drive train. According to of this embodiment, in response to the determination of a defect in at least two sensors, the adjustment of the braking and/or driving effect at the wheels assigned to these sensors is activated as a substitute as a function of the detected rotation quantity. According to this embodiment, the case in which two speed sensors are defective is advantageously taken into account. In this case, a rotation quantity in the drive train is used as a substitute quantity. With this substitution by the rotation quantity, it is possible to take into account a corresponding gear ratio acting-in the drive train and/or the efficiency of the drive train and/or a slip of a clutch arranged in the drive train and/or the operating state of a torque converter arranged in the drive train.
In a further modification of the present invention, an acceleration quantity representing the vehicle""s longitudinal acceleration is detected. In this case also, defects in the speed sensors are determined. According to this modification of the present invention is that in response to the determination of a defect in one sensor, the adjustment of the braking and/or driving effect at the wheel of an axle assigned to this sensor is activated as a substitute as a function of the detected acceleration quantity. In this connection, it is provided in particular that the acceleration quantity is integrated and the integrated acceleration quantity is used as a substitute. A suitable substitute quantity for wheel rotational movement is obtained in this manner via the longitudinal acceleration. In this embodiment of the present invention, it can be provided that the acceleration quantity and/or the integrated acceleration quantity is corrected as a function of the angle of inclination of the vehicle in longitudinal direction.
In a third modification of the present invention, a rotation quantity is also detected which represents a rotational movement in the drive train. Furthermore, defects in the sensors are also determined in this case. According to this modification, in response to the determination of a defect in one sensor, the adjustment of the braking and/or driving effect at the wheels assigned to these sensors is activated as a substitute as a function of the detected rotation quantity.